The invention relates to a metering apparatus of a reaction molding machine, more particulary to an apparatus for metering components such as reactant and or filler material components for use in a reaction injection molding machine.
A metering apparatus of this type is known from the prospectus "Polyurethane-Filler Metering Technology . . . " of June, 1978 of the Krauss-Maffei AG (figures on pages 2 and 4). In this metering apparatus, the cylinder walls of the metering cylinder and the cylinder walls of the hydraulic drive means to drive the metering piston are joined together in a single piece. The metering piston comprises a sealing unit and the devices for the retightening of the packing, which are accessible through orifices in the cylinder walls of the metering cylinder.
This metering apparatus has the disadvantage that when the metering piston is dismantled for maintenance, replacement of the sealing unit, and inspection of the inner walls of the cylinder, it is also necessary to remove the hydraulic drive unit from the one-piece cylinder. The piston of the hydraulic drive unit, which is joined to the metering piston, is a long and massive structural component which requires a crane for its removal. A metering apparatus of this type also has a considerable structural height, so that a correspondingly high space must be provided above the metering apparatus for its disassembly. Inspecting the metering cylinder is rather difficult, because it is accessible only through the orifice in the hydraulic drive unit.
Piston metering devices are already known in which two hydraulic cylinders of a hydraulic drive unit are provided in addition to the metering cylinder. Such a unit has a reduced structural height, but represents a more expensive construction because the metering piston must be connected by means of a yoke with the two hydraulic pistons of the hydraulic drive unit.